A medical X-ray examination apparatus with an imaging device is already known from the patent U.S. Pat. No. 5,467,380 (de Jonge et al). The imaging device produces a sequence of images and includes a system for processing the images of the sequence so as to reduce the noise. This system includes first recursive temporal filtering means which form a sum of an already temporally filtered image and a difference image which is weighted by a recursion factor. This recursion factor is provided by a table and is inversely proportional to the difference whereto it is applied. The difference image is formed by calculation, at points of given location, of the intensity differences between the noisy image to be treated and a preceding image which has already been temporally filtered. This system also includes motion detection means which are formed by a comparator which compares the intensity differences in the difference image with a noise threshold and signals the presence of a moving object when a difference in the difference image exceeds this threshold. This system also includes spatial filtering means for providing, on the basis of the noisy image, an image smoothed by low-pass filtering. Finally, this system includes means for forming the sum of said image smoothed by low-pass filtering and the recursively temporally filtered image, said images being assigned respective weights which favor either the spatially filtered image, in the case where a moving object has been detected, or the temporally filtered image in the opposite case.
A problem is encountered in that in the known system intensity differences due to the noise peaks cannot be distinguished from those which are due to the movements. Another problem consists in that this known system outputs a low-pass smoothed image instead of a temporally filtered image in case a moving object has been detected; such low-pass spatial filtering, applied directly to a noisy image, blurs the contours so that small objects in motion may be lost.
Citation of a reference herein, or throughout this specification, is not to construed as an admission that such reference is prior art to the Applicant's invention of the invention subsequently claimed.